1. Field of the Invention
The present invention relates to an impeller, and more particularly, a centrifugal impeller utilized for a compressor of, for example, a turbo-charger.
2. Related Art
There is known a centrifugal impeller of the type mentioned above such as disclosed in Japanese Utility Model Laid-open Publication No. HEI 2-132820, for example. A turbo-charger disclosed in this publication is provided with a turbo-wheel driven by an energy of an exhaust gas from an engine of the turbo-charger, and the turbo-wheel is coupled with an impeller through a rotating (rotational) shaft so that the driving force of the turbo-wheel is transmitted to the impeller through the rotating shaft to rotate the impeller, and according to the rotation of the impeller, intake pressure on the intake (air-suction) side of the engine is increased and then supplied to the engine.
Such impeller is formed with a thickness reduced portion on a back side of a disc on which blades or vanes are formed so as to reduce a thickness between front and back surfaces of the disc and also formed with a boss or boss portion so as to protrude from such thickness reduced portion towards the back side of the disc, and a rib is formed so as to extend in the radial direction between the boss and the back surface of the disc.
According to the formation of such thickness reduced portion on the back surface side of the disc, a weight of the impeller is reduced and possibility of generation of defect at a time of resin molding process is reduced. Moreover, the formation of the rib extending in the radial direction between the boss and the back surface of the disc can preferably suppress deflection of the disc and displacement in the peripheral direction of the boss.
However, in such impeller structure as mentioned above, since a plurality of ribs are formed along the radial direction, when the impeller is rotated at a high speed, the ribs constitute resistance and, hence, generate aerodynamic load. In addition, since the ribs and the thickness reduced portion are alternately formed to portions around the boss portion, it is difficult to feed the resin uniformly to the peripheral edge portion of the impeller at an injection molding process using a mold.